Along with the popularization of the big-screen multifunctional mobile terminal, the mobile data service is applied more and more widely; the demands for mobile communication are not limited to telephone, message and mobile terminal web browsing service. Since the fast development of the Internet, there emerges a large number of multimedia services. Various kinds of high-bandwidth multimedia services such as video conference, television broadcast, video on demand, advertisement, web education and interactive game are ceaselessly emerging, which satisfies the ever increasing service demand of mobile users on the one hand, and brings a new service growth point to the mobile operators at the same time. Such mobile multimedia services require the multiple users to receive the same data simultaneously, compared with the ordinary data services, the mobile multimedia services are featured with large data quantity, long time duration, and high sensitivity of time delay.
To utilize the mobile network resources effectively, the 3rd generation partnership project (referred to as 3GPP) proposed the multimedia broadcast multicast service (referred to as MBMS); a point-to-multipoint service is provided for a data source to transmit data to multiple users in the mobile network, so as to realize network resource sharing, and improve the utilization ratio of network resources (especially the valuable air interface resources). The MBMS is a technique for transferring data from one source to multiple destinations by sharing the network resources. The MBMS defined by the 3GPP can implement not only the low speed message type multicast and broadcast for the plain text, but also the multicast and broadcast of the high speed multimedia service, and provide a plenty and variety of video, audio and multimedia services; therefore, the MBMS has become a trend of development, and provides a better business prospects for the development of the 3G and the 4G.
There are two kinds of RSs currently under discussion; one is a transparent RS, the other one is a nontransparent RS; these two kinds of RSs are hereinafter described in detail.
The transparent RS: in the transparent relay mode, the RS and the user terminals (referred to as UTs) are all located within the range covered by the multihop relay base station (referred to as MR-BS), at the same time, the UTs are also located within the range covered by the RS. The downlink control information and the data service are transmitted independently, wherein, the downlink control information is directly transmitted from the MR-BS to the UTs without passing through any RS, while the data service is transmitted to the UTs via an RS. The RS does not transmit its information such as synchronization information, system configuration information and resource allocation information in the downlink broadcast channel. All the RSs and UTs belonging to the same MR-BS cell achieve the synchronization with the MR-BS via the synchronization channel (referred to as SCH) of the MR-BS. In the transparent relay mode, the UT is unaware of the existence of the RS (although there is communication between the UT and the RS). The transparent relay RS is mainly used for improving the system capacity and the throughout of individual user, and it only supports the centralized scheduling especially in the urban areas, the transparent RS and the nontransparent RS can coexist in a multihop relay cell (referred to as MR-cell).
The nontransparent RS: in the nontransparent relay mode, the RS is located within the range covered by the MR-BS while the UT is located outside of the range covered by the MR-BS, the UT, however, is located within the range covered by the RS. The downlink control information and the data service must be both transmitted to the UT via the RS. The RS transmits its synchronization information, system configuration information, resource allocation information and so on in the downlink broadcast channel. In the nontransparent relay mode, the UT can detect the existence of the RS. The nontransparent relay RS is mainly used for improving the coverage of the system, and it can support the centralized scheduling and also can support the distributed scheduling especially in the suburban areas. In an MR-cell, the transparent RS and the nontransparent RS can coexist.
To sum up, the transmission of the MBMS service with the participation of the transparent RS in the next-generation communication system has not been realized at present.